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Issue 5, 2014
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The Houk–List transition states for organocatalytic mechanisms revisited

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Abstract

The ten year old Houk–List model for rationalising the origin of stereoselectivity in the organocatalysed intermolecular aldol addition is revisited, using a variety of computational techniques that have been introduced or improved since the original study. Even for such a relatively small system, the role of dispersion interactions is shown to be crucial, along with the use of basis sets where the superposition errors are low. An NCI (non-covalent interactions) analysis of the transition states is able to identify the noncovalent interactions that influence the selectivity of the reaction, confirming the role of the electrostatic NCHδ+⋯Oδ interactions. Simple visual inspection of the NCI surfaces is shown to be a useful tool for the design of alternative reactants. Alternative mechanisms, such as proton-relays involving a water molecule or the Hajos–Parrish alternative, are shown to be higher in energy and for which computed kinetic isotope effects are incompatible with experiment. The Amsterdam manifesto, which espouses the principle that scientific data should be citable, is followed here by using interactive data tables assembled via calls to the data DOI (digital-object-identifiers) for calculations held on a digital data repository and themselves assigned a DOI.

Graphical abstract: The Houk–List transition states for organocatalytic mechanisms revisited

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Publication details

The article was received on 12 Dec 2013, accepted on 24 Feb 2014 and first published on 24 Feb 2014


Article type: Edge Article
DOI: 10.1039/C3SC53416B
Citation: Chem. Sci., 2014,5, 2057-2071
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    The Houk–List transition states for organocatalytic mechanisms revisited

    A. Armstrong, R. A. Boto, P. Dingwall, J. Contreras-García, M. J. Harvey, N. J. Mason and H. S. Rzepa, Chem. Sci., 2014, 5, 2057
    DOI: 10.1039/C3SC53416B

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